The invention herein disclosed was made in the course of or under a contract or subcontract thereunder with the Department of the Air Force.
The present invention relates to a method of treating a semiconductor device in order to improve certain electrical characteristics of the device.
It is known that in the making of semiconductor devices the various processing steps, particularly those which are carried out at high temperatures, often result in adversely affecting certain performance characteristics of the devices, such as the minority carrier lifetime and the current leakage properties of the devices. It is believed that these adverse effects are the result of either the redistribution or precipitation of certain contaminants in the semiconductor device. Such contaminants may be in the form of heavy metal impurities, such as gold, copper and iron, or alkali metals, such as sodium, potassium and calcium.
To overcome the problems raised by those contaminants, various techniques have heretofore been used to either prevent the contaminants from initially entering the semiconductor device and/or removing the contaminants from the semiconductor device, preferably at or near the end of the manufacturing process. To prevent the contaminants from initially entering the semiconductor device "clean handling" techniques have been used. These techniques require careful cleaning of all materials and equipment, and the carrying out of manufacturing and assemblying operations in a dust-free laminar flow atmosphere. Although these techniques are effective, they are cumbersome to employ and expensive because of the requirements for constant vigilance, contamination measurements and personnel indoctrination.
To remove the contaminants from the semiconductor device various techniques for gettering and/or out-diffusing the contaminants have been used. Such techniques include heat treatment with a phosphorus oxide glass layer on the semiconductor device or processing the semiconductor device with nickel or a nickel alloy in contact with the device. Each of these techniques has the disadvantage that it requires coating the semiconductor device with an additional material which forms no part of the active portion of the semiconductor device and can even be detrimental to the active portion of the semiconductor device. For example, the heat treatment with a phosphorus oxide glass layer can cause the diffusion of phosphorus, an N type impurity, into the semiconductor device resulting in an N type surface region which would have to be removed by etching.
Another technique which has been developed to remove the contaminants from a semiconductor device and to improve its lifetime characteristics is to heat the semiconductor device while exposed to an atmosphere containing hydrogen chloride. This technique is described in U.S. Pat. No. 3,556,879 to A. Mayer, issued Jan. 19, 1971 entitled "Method of Treating Semiconductor Devices" and in U.S. Pat. No. 3,556,880 to F. P. Heiman etal, issued Jan. 19, 1971 entitled "Method of Treating Semiconductor Devices to Improve Lifetime". Although this technique is very satisfactory for removing contaminants and improving lifetime characteristics, it does have a disadvantage of a relatively high time X temperature factor. That is, to achieve a satisfactory treatment in a short period of time it must be carried out at a relatively high temperature or if a low temperature is used the treatment must be carried out for a relatively long period of time. This high time X temperature factor of this technique can be detrimental to certain types of semiconductor devices.